Process of making pigments



' LE'ROY BAKER.

PROCESS OF MAKING PIGMINTS. APPLICATION FILED AUG-I3. I920.

. Patented Aug. 8,1922.

"entree stares earsnr entice.

LE ROY BAKER, OF ST. LOUIS, MISSOURI.

PROCESS OF MAKING PIGMENTS.

. Specification of Letters Patent.

Original application filed July 16, I919, Serial No. 311,296. Divided and this application filed August '13, 1920. Serial No. 403,209.

T 0 all whom it may concern.

Be it known that I, Ln Ror BAKER, a citizen of the United States. and resident of St. Louis. and State of Missouri, have invented certain new and useful lmprovementsin the Processes of Making Pigments, of which the following is a specification containing a full, clear, and exact description, reference being. had to accompanying drawings, forming a part thereof. I

lily invent-ion relates to certain new and useful improvements in the process of making pigments and especially relates to making a sun-proof zinc white pigment.

The accompanying drawing illustrates a conventional form of apparatus by means of which my process may be carried out; this application being a division of my applica tion filed July 16th, 1919, Serial No. 311,296.

in carrying out my process I place a solution of commercial or impure zinc sulphate in the tank l, in which is located a mechanical agitator 2, and the tank 1 is connected with a source of compressed air supply 3 and with a source of steam supply through the valve controlled steam inlet pipe 4.

The. zinc sulphate solution contained in tank 1 is heated with steam at or near the boiling point. After the solution has been heated by steam, or by any other suitable agency, 1 admit air under pressure into the solution from the compressed air tank 3. By means of this bubbles of air are blown through the solution. The purpose of heating the Zinc sulphate solution is to make it more active and more susceptible to the oxygen in the air bubbles.

During the time the zinc sulphate solution is being treated with steam and compressed air, I add to the ZlllC- sulphate solution a metallic peroxide (such .as 'calcium or barium) in powdered form. in sufficient quantity to remove the iron present. and I also add to the solution a monoxide (such as zinc oxide or lead oxide) in powdered form, and in the proportion of about one per cent by weight of the Zinc sulphate in the solution, it being understood. of course, that I can add any other suitable metallic monoxide. It will be noted in this connection that barium peroxide will precipitate iron, either hot or cold from solutions containing it. Some basic ferric sulphate is formed. Barium peroxide is only slightly decomposed by boiling water, unless a long time or a concentrated amount is taken. Such decomposimixed together.

tion throws down Zinc hydrate from the zinc sulphate solution, which in turn reacts with iron sulphate. After the foregoing treatment, by means of a pump'such as5. I trans fer the solution from the tank 1 into the filter press 6 for the purpose of removing the iron oxide which has been precipitated from the iron sulphate contained as an impurity in the zinc sulphate solution, and then conduct the filter pressed solution into another tank 7 which is also connected with a steam and compressed air supply. After the solution has reached tank 7 Isubiect it to the same treatment that it was subjected to in tank 1, and then transfer this solution by pump 7 to another filter press 8, and from this'filter press the solution is transferred to tank 9 or storage tank, the zinc oxide having passed into the hydrated form,

passes through the filter with the liquor as a fine silky precipitate.

I then take a solution of barium sulphide contained in the tank such as 10 and allow the treated solution in tank 9 and the ba rium solution in tank 10 to flow into a mixing tank 11. In this tank 11 the treated sulphate solution and the barium solution are This precipitates the sulphate solution as the two metallic salts mutually precipitate each other.

After this operation, 1 take the solution from tank 11 and transfer it by means of a pump 12 into another filter press 13. After this the filter pressed precipitated pigment is washed, dried, calcined, quenched in cold water, ground wet, again washed and again filter pressed, then dried and packed for the market.

I have discovered by experiment that in the manufacture of pigments wherein a metallic peroxide is used alone that the batch of pigment was not sun-proof. I further discovered that by adding a monoxide which precipitates zinc in a hydrated form that the pigment was permanent under all light conditions.

Having fully described my invention what I claim is:

1. The process of making pigments which consists in subjecting a solution of Zinc sulphate to the action of airrunder pressure and steam in the presence of a slightly soluble metallic peroxide and a lead mono-oxide filter pressing said solution, and lastly precipitating said solution with a solution of barium sulphide.

3. The herein described process of making meme? pigments which consists in precipitating a solution of pure zin c'sulphate with a, 501111- 10 ti'on of barium sulphide in the preeenceof 4 zinchydrate. In testimony whereof, I have 'signedsmy name to this specification.

LE :eeY BAKER. 

